1. Technical Field of the Invention
The present invention relates to law enforcement agency. surveillance monitoring of a mobile station operating within a cellular telephone network and, in particular, to controlling the monitoring of a marked mobile station at instances of inter-exchange hand-off.
2. Description of Related Art
It is well known in the art for law enforcement agencies to tap telecommunications trunk connections for the purpose of monitoring voice conversations (calls or communications), signaling data, short message service messages and the like. Telecommunications switches in the network are programmed with a stored list of telephone numbers assigned to subscribers whose use of the network is to be monitored. Whenever a switch handles a communication connection set-up from/to a calling/called party (or message delivery, or signaling activity) where the calling party or called party identification number matches a number on the stored list, the switch requests the establishment of a trunk connection (comprising the tap) with a monitoring center. If the request is granted, a tap trunk connection is established with the monitoring center and then connected (in a manner much like the formation of a conference or three-way call) into the subscriber call connection.
This conventional well known technique for triggering an opportunity for law enforcement agency monitoring is applicable generally speaking solely to the setting up of a communication to/from a marked called/calling party. If the call is initially handled at set-up by a switch that has marked the called/calling party for monitoring, then the tap is established and the surveillance takes place (typically for the duration of the communication). If, on the other hand, the switch at call set-up does not have the called/calling party marked, the tap is not requested and no surveillance occurs for the remainder of that communication.
One problem experienced with this conventional approach for triggering law enforcement monitoring arises when a non-monitored communication is subsequently served, following the occurrence of an inter-exchange hand-off, by a switch where one of the called or calling parties is marked for monitoring. Historically in this case, because no monitoring was initially established in response to the communication at set-up, no surveillance monitoring occurs after the inter-exchange hand-off because the hand-off does not constitute a communication set-up event that would trigger a request for a tap connection. There is a need for a mechanism to control law enforcement monitoring to trigger the establishment of the tap connection in such cases.
Another problem arises with respect to the duration of the monitoring. Conventionally, such monitoring, once started, continues until the communication is terminated. However, if the monitored communication undergoes an inter-exchange hand-off from a jurisdiction where such monitoring is lawfully authorized to a jurisdiction where the monitoring is not authorized, the continuation of monitoring following hand-off may violate the law and jeopardize the material information lawfully collected before hand-off. There is a need for a mechanism to control or inform law enforcement monitoring to (if necessary) terminate the tap trunk connection in respect of such jurisdictional (legal) limitations to lawful monitoring.
A mobile station cellular communication that is not currently being monitored by a law enforcement agency undergoes an inter-exchange hand-off. A target exchange for that hand-off responds to a facilities request from an anchor exchange by first determining that a party to that communication has been marked for law enforcement agency monitoring and then establishing a tap connection to a law enforcement agency monitoring center to begin monitoring of that communication following the completion of the inter-exchange hand-off. For an inter-exchange hand-off of a law enforcement agency monitored mobile station cellular communication, on the other hand, the target exchange for that hand-off first determines that law enforcement agency monitoring of that communication is not lawfully authorized with respect to the target exchange and then sends a tap connection termination message back to an originally handling exchange (the anchor) instructing the anchor exchange to terminate its tap connection with a law enforcement agency monitoring center following the completion of the inter-exchange hand-off. In each case, mobile station party location information may be collected by an exchange and delivered to the law enforcement agency monitoring center. Additionally, information may be provided from the exchanges to the law enforcement agency monitoring center indicating that the actions taken (establishing or terminating the tap connection) are being taken in response to an inter-exchange hand-off.